Insulin resistance stands as a significant threat to public health worldwide, and a largely unmet medical need. To unravel the complex biology of this protean syndrome, we have endeavored to apply genetic techniques to probe gene function and tissue interactions related to metabolism, and identify tractable targets for pharmacological intervention in type 2 diabetes. Over the past five years, the notable contributions of this grant to our knowledge of the insulin resistance syndrome have been: (i) a critical reassessment of the relative roles of insulin-dependent and -independent mechanisms of glucose disposal in metabolic homeostasis; (ii) the discovery of mechanisms by which non-canonical sites of insulin action, such as central nervous system (CNS) and endocrine pancreas, play an early and decisive role in the progression from insulin resistance to diabetes; and (iii) the notion that pancreatic ? cells are an insulin-sensitive cell type. Building on these lessons, the Pl proposes studies of the integrated physiology of insulin action that will focus primarily on the contribution of CNS, liver and enteroendocrine system to the insulin-resistant state. The Pl presents data putatively identifying an insulin-sensitive neuron population, characterized by Glut4 expression; as well as a novel gut epithelial progenitor cell with the unique ability to give rise to bona fide insulin-secreting , ?-like endocrine cells in vivo. Three aims are outlined: Aim 1 will tackle the role of insulin signaling in brain glucose metabolism, using a novel approach to identify Glut4- expressing neurons and characterize their contribution to systemic metabolism. Aim 2 will delve into the pathophysiology of hepatic insulin resistance, and specifically into the identification of transcription factors that cause the paradoxical admixture of increased glucose production and triglyceride synthesis that characterizes the diabetic liver. Aim 3 will study the role of insulin signaling in a newly identified sub population of gut epithelial progenitor cells that express the insulin-regulated transcription factor Foxo1 and show the surprising ability to be reprogrammed into ?-like cells that secrete insulin in response to glucose The proposed body of work will advance our understanding of the insulin-resistant syndrome at the biochemical, genetic, and integrated physiological levels, with the ultimate goal of translating newly acquired information into innovative approaches to its treatment.